Method of producing blocking layer devices



NOV. 16, 1943. c, w, HEWLETT 2,334,554

METHOD OF PRODUCING BLOCKING LAYER DEVICES Filed June 22, 1942 Conductive Base Produce Layer lVo. of' Ha/agen Containing Se/enium Produce Layer No.2 of

Halogen free Selenium Vitreous Form Con vert Layer No. 2.

Crystalline Form Produce B/ocking Layer on Layer No.2.

Clarence W. H ewlett,

His Attorney.

Patented Nov. 16, 1943 METHOD OF PRODUCING BLOCKING LAYER DEVICES Clarence W. Hewlett, Schenectady, N. Y., assilnor to General Electric Company, a corporation of New York Application June 22, 1942, Serial No. 447,943

6 Claims.

The present invention relates to an improved method for producing blocking layer devices and more particularly for producing dry plate rectifiers of the selenium type.

It is a principal object of the invention to produce selenium blocking layer cells which are characterized both by extremely low resistivity in the forward direction and by extremely low conductivity in the reverse direction, thereby asstu'ing high operating efliciency.

It has been observed that the forward resistivity of selenium may be reduced by incorporating in it a small quantity of a halogen (i. e., chlorine, bromine, iodine, or fluorine). However, this has the objectionable ancillary effect of making it diflicult to produce a satisfactory blocking layer on the halogen-containing selenium. This latter difficulty may be to some degree lessened by applying a quantity of pure selenium over the halogenated material before the blocking layer is produced, this being a step which is suggested for a somewhat different purpose in F. Brunke Patent No. 2,189,576, granted February 6, 1940. I have found, however, that when produced by conventional methods of procedure, a pure selenium layer superimposed on a layer of halogenated selenium tends to separate and peel off, resulting in the production of an inferior or unsatisfactory cell.

I have discovered that the difilculties noted in the foregoing may be overcome and a rectifier of high efliciency obtained by applying the two selenium layers in different ways, the first, or halogen-containing layer, being formed under conditions which assure the deposition of the selem'um in crystalline form, and the second, halogen-free layer, being initially produced in vitreous form and thereafter converted into the crystalline form. This procedure assures not only that the second selenium layer shall be strongly adherent but also that the composite layer structure shall be of non-porous character-a circumstance which is highly desirable from the standpoint of avoiding excessive reverse current. Moreover, the last-deposited layer proves to be well adapted to having a blocking layer developed on its surface.

The features of the invention desired to be protected herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 is a diagram invention, and Fig. 2 is a sectional view of a blocking layer rectifier produced in, accordance with the invention.

A blocking layer device of the type under consideration comprises a series of appropriately constituted layer which are successively produced on a conductive base adapted to serve as a carrier electrode. Such a base is indicated at I in Fig. 2, and may consist, for example, of aluminum or iron or of an alloy of aluminum and iron. The base is preliminary coated with a contact-improving substance such as bismuth, indicated in the drawing by the layer 2, and is thereafter successively covered with other layers 3 to 6, the nature of which will be brought out in the following.

In accordance with the present invention, the layer 3 is formed as a crystalline deposit of halogen-containing selenium. This may be accomplished, for example, by initially maintaining the base member at a temperature on the order of to 120 degrees C. (preferably about degrees) while exposing the member to the vapor of selenium which contains a halogen, preferably chlorine, to the extent of about .06 to .015 per cent, or about one atom of halogen in 800 to 3200 atoms ,of selenium. The selenium which is laid v down in this way will, at the temperature specified, condense in the bright, crystalline form. After th formation of the layer 3 as above described, the coated base is next brought to a temperature on the order of 6' to 80 degrees C. (preferably about 70 degrees) and while at this temperature is exposed to vaporized selenium which is free of halogen. At this lower temperature, selenium will condense on the base member to form a layer which is of the glossy black or vitreous modification. The device is then placed in an oven and maintained at a temperature above 200 degrees C. (i. e., in the neighborhood of 210 to 215 degrees C.) for 40 to 60 minutes, after which it is rapidly cooled to room temperature. This last step has the effect of melting the vitreous selenium comprising the layer 4 and causing the melted selenium to fuse into an imperforate film, thus sealing any small openings which may initially have existed in this layer or in the layer 3. After fusion and during continued heating, the vitreous selenium solidifies and finally becomes converted to the bright crysstalline form, in which form it is ready for the application of the blocking layers. The blocking layer, indicated at 5, is suitably produced in the manner described in my prior application, Serial showing the procedural steps employed in the 66 No. 423.562, filed December 18, 1941, by subjecting the layer 4 to the oxidizing action of hydrogen peroxide for an appropriate period. Finally a counter-electrode 6 is superimposed on the blocking layer by spraying on a thin layer of soft solder or the like.

In the production of a rectifier cell according to the foregoing procedure, the halogenated selenium layer 3 may appropriately be made about 1.2 to 1.6 mils in thickness and the pure selenium layer 4 about 0.3 to 0.4 mil in thickness. The relative resistivity of the halogenated selenium is so low that the overall resistance of the composite layer is very little greater than that of the layer 4 alone. However, the greater thickness of the composite layer, as well as the fact that it is laid down in two successive deposits with the last layer being fused in the course of its formation, assures that there shall be no unduly thin or weak spots in the layer through which excessive inverse currents might flow.

If the halogenated layer 3 be applied in the vitreous form (either by applying as a paste or by evaporating while maintaining the base member at a low temperature) and then crystallized by heat treatment, it is found that the layer 4 adheres poorly, frequently peeling of}? in places. However, by applying the first layer directly in the crystalline modification by condensing it on a base which is held at a temperature in the neighborhood of 100 degrees C., as specified above, satisfactory adherence of the subsequently deposited pure selenium is obtained. The fact that the layer 3 is already in the crystalline modification during the process of forming the layer 4 also avoids melting the first-named layer and prevents diffusion of its halogen component into the pure selenium, where it would prevent the production of a satisfactory blocking layer. The overall result of the procedure described is that the rectifying cells produced are of high conductivity in the forward direction and of extremely low conductivity in the inverse direction so that the operating efficiency of the cells produced is high.

The vaporizing steps referred to in the foregoing may be carried out in one way by the use of the apparatus described in my copending application, Serial No. 423,561, filed December 18, 1941.

While the invention has been described with reference to a particular embodiment, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of producing a blocking layer device on a conducting base, which method comprises depositing selenium containing a halogen on said base from a vapor directly to the crystalline state, depositing on said layer a layer of halogen-free selenium in vitreous form, converting said last-named layer into crystalline form, and thereafter producing a blocking layer on the last-named layer.

2. The method of producing a blocking layer device on a conducting base, which method comprises depositing a layer of halogen-containing selenium on said base under temperature con ditions which assure the deposition of said selenium in crystalline form, depositing a layer of halogen-free selenium on said first-named layer under temperature conditions which assure the deposition of said second layer in vitreous form, converting said second layer into the crystalline form by the application of heat, and thereafter producing a blocking layer on said second layer.

3. The method of producing a blocking layer rectifier on a conductive base which method comprises depositing halogen-containing selenium on said base while maintaining said base at a temperature between and 120 degrees C., thereafter depositing a layer of haloge -free selenium on said first layer while maintaining the base at a temperature in the neighborhood of 60 to 80 degrees 0., thereby to assure deposition of the second layer in vitreous form, thereafter heating said base to above 200 degrees C. to con vert said second layer into the crystalline form. and finally producing a blocking layer on said second layer.

4. The method of producing a blocking layer" rectifier on a conducting base which method comprises initially maintaining said base at a temperature on the order of degrees C., while subjecting the base to vaporized selenium which contains about .015 to about .06 per cent of chlorine, thereafter maintaining said base at a temperature on the order of 70 degrees C. while subjecting it to the vapor of chlorine-free selenium, reheating to a temperature above 200 degrees C., and finally subjecting the selenium-treated surface to an oxidizing agent to provide a blocking layer.

5. The method of fabricating an electric contact rectifier which consists in heating a conductive base to a temperature of about 100 to C., depositing halogenated crystalline selenium on said base, applying a vitreous layer of substantially pure selenium on said crystalline selenium, converting said vitreous selenium to a crystalline state, oxidizing the exposed surface of such second layer to produce a blocking layer thereon, and finally applying a counter electrode on said blocking layer.

6. The method of fabricating a solid element contact retifier which consists in heating a conductive base to a temperature of about 100 to 120 C., exposing said base to the vapor 0f selenium containing about .015 to .06 per cent of chlorine, thereby causing selenium containing chlorine to be deposited in the crystalline state, discontinuing such deposition when the thickness of such crystalline layer is about 1.2 to 1.6 mils, applying a layer of pure vitreous selenium about 0.3 to 0.4 mil in thickness over said crystalline layer, heating the composite body thus formed to a temperature of about 210 to 215 C. for a sumcient length of time to result in the conversion of said vitreous layer to the crystalline state, producing a blocking layer thereon by oxidation and applying a counter electrode to said blocking layer.

CLARENCE W. HEWLETT.

CERTIFICATE OFQCOIRRECTION,

' November 16, 1911.5. CLARENCE w. Emma-T.

of the above hfimbered patent requiring correction as fo lloyvs Page 1, sec. 0nd column, line 11, for preliminary r'ead -pre11m1nar1.ly--;-l1n 32',

' for "61:0 read '60 to 80; page 2-, second column, line 52,- for 'r'etifier" read 1 -ect1fier--; and that the said Letters Patent should be read case in the Patent Offl'ce. V I

Signed ma sealed this 11th day of January, A; 1). 19%.

I Henr y- Van Arsdale, (30:11) Acting commissioner OfPatentS 

